A study on the Reuse of Purified Wastewater for Agriculture

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In Japan, the rural sewerage projects are being actively carried out. On the other hand, it is afraid that we are running short of water. Thinking of the rural sewerage treatment, we can understand that the construction of sewage plant is the construction of recycling plant of water in a sense. The sludge is always produced as the results of purification of sewage in the plant. But, the sludge is hated as dangerous and troublesome matters by people. In the old time, night soil was used by farmer for agriculture. But, as the chemical fertilizers are being produced, human manure is disliked and is not paid attention to. Therefore, it leads to environmental problems in many places. Reviewing agricultural field, as supply of organic matter to agricultural fields was stopped and only the chemical fertilizer were used, the field has lost the fertility. Then we started the study to reuse the purified wastewater to solve the shortage of water, and to use the composted sludge as organic fertilizer to enrich soil. It is concluded from our study that (1) the purified wastewater can be recycled as irrigation water equivalent to drinking water, (2) the composted sludge used and valued high as organic fertilizer. It is not to say that the exact check has to be done if both of the recycled water and sludge meet the environmental standard or not before their reusing.